i found this in a different article

John Fea: For much of the twentieth century, evangelicals leaned Republican. For example, during the 1950s, as Princeton historian Kevin Kruse has shown, white evangelicals gravitated toward the civil religion of Dwight Eisenhower and the postwar religious revival. During the 1960s, Richard Nixon used Billy Graham to help him win over white evangelicals. But it was not until the late 1970s and 1980s that white conservative evangelicalism became fused with the GOP. The result of this merger is what we call the “Christian” or “Religious” Right today. This political movement was born out of fear that the removal of prayer and Bible reading in schools, the growing diversity following the Immigration Act of 1965 (Hart-Celler Act), the intrusion of government (“big government”) into segregated Christian academies in the South, and the legalization of abortion were undermining America’s uniquely Christian identity. The leaders of the Christian Right believed the best way to “reclaim” or “restore” this identity was by gaining control of all three branches of government. Jimmy Carter, a self-proclaimed “born-again Christian,” was not championing these issues to the degree that many evangelical conservatives wished. As a result, white evangelicals gravitated to Ronald Reagan, a man who seemed to understand evangelical concerns, or was, at the very least, willing to placate evangelicals.

2. Considering the longer history of evangelical politics, were there forces of change—both within evangelicalism itself, as well as in American culture and politics writ large—that politically stirred evangelicals in the long lead-up to 2016 in unique and unprecedented ways? Stated another way, was 2016 a pivot in the life of modern evangelicalism and its political expressions and ambitions, or a continuation of existing—perhaps accelerating—trends within the movement? Griffith: Both-and. The 2016 election was certainly a continuation of existing anti-feminism; the hatred of Hillary Clinton goes back to 1992 and her perceived insult to traditional stay-at-home women (“Well, I guess I could have stayed home and baked cookies …”). There is a lot to say about this! On the other hand, I also think there was an acceleration of forces such as fear and anger toward both immigrants of color and citizens of color that appeared to mobilize conservative religious voters to an extraordinary degree. Scholars are still parsing this out, of course, and debating the politics of race in white evangelical voting patterns; but there’s no question that white working-class men in many communities have adopted a narrative of victimization in which they are being left behind and displaced by “outsiders” (people of color, immigrants, etc.). A large number of white women seem to support this view and identify with these men’s victimization; I suppose they find some measure of comfort in that narrative, even if it fuels their anger and paranoid fear of outsiders. So what journalists keep seeing locally and calling “economic anxiety” is deeply tied up with racist fears of who the culprits are. This is in no way limited to evangelicals, but many of those who are expressing this sense of victimization are evangelicals, hearing these narratives from pulpits like that of Robert Jeffress and other Trump supporters. The evangelical belief that one is “in but not of the world” and has thus willingly taken on the status of a visitor to this evil world lends itself pretty seamlessly to a sense of one’s own victimhood. Fea: Fear, the pursuit of power, and an approach to public policy built on an unhealthy dose of nostalgia have plagued evangelical politics for a long time. Since the 1970s, the Christian Right has followed a well-known political playbook. Its members want to elect the right president of the United States who will appoint the right Supreme Court justices who will then overturn decisions that the Christian Right believes have undermined the republic’s Christian foundations. In the past, this playbook was inseparable from the moral character of the candidate. In 2016, however, the Christian Right executed the playbook in support of a candidate known for his sexual escapades, nativism, deceit, xenophobia, racism, and misogyny. This is a new development. The playbook survived despite the candidate. This is a testimony to the playbook’s power and the role that Christian Right leaders such as Jerry Falwell and Pat Roberston played in reshaping American political culture.

But looking for an EXACT DATE (if we are talking about exponential increase in modern time) we find it to be Feb 1st 1953 as it is shown here: history.com/…/eisenhower-billy-graham-religion-in…

On February 1, 1953, just 10 days after his inauguration, Eisenhower was baptized and welcomed into the National Presbyterian Church by the Rev. Edward Elson. Eisenhower remains the only president ever to have been baptized while in office, and his work to link faith and American identity has influenced political debate in the country for half a century since.

Though the baptism ceremony itself was private, Eisenhower made every effort to place faith at the center of national life during his years in office. He began his inaugural address with a short prayer that he had written himself. His Cabinet meetings began with a moment of silent prayer. He initiated the National Prayer Breakfast, and welcomed Rev. Billy Graham into the White House as a spiritual adviser. He heartily approved when, in 1954, Congress inserted “under God” into the Pledge of Allegiance and later made “In God We Trust” the official motto of the United States, even placing these words on the paper currency.

Why so much religiosity? Eisenhower believed religious faith was the single most important distinction between American freedom and Communist oppression. The Soviet bloc was a tyrannical state that sneered at spirituality. Americans of the Judeo-Christian tradition, by contrast, held to the belief that every person was God’s creation. Individual human rights were therefore divine and not to be trampled underfoot by an all-powerful government. To wage and win the Cold War, Eisenhower believed, Americans must be dedicated to that principle.

On Sunday, February 7, 1954, Eisenhower gave a radio address that emphasized the importance of Godliness and spirituality in American history. “Out of faith in God, and through faith in themselves as His children, our forefathers designed and built the Republic,” Eisenhower said. The president gave a brief civics lesson that recalled the struggles of the Pilgrims, the testing of George Washington at Valley Forge, and the determined battle of Abraham Lincoln to save the Union: All of these men shared a steadfast belief in God.

The one unifying feature of the American experience, Eisenhower insisted, was faith—“by the millions, we speak prayers, we sing hymns, and no matter what their words may be, their spirit is the same: In God is our Trust.” At a time of surging popular piety, many Americans welcomed this kind of spiritual direction from their president.

Eisenhower was not the only American making the case for religion in the public sphere. The 1950s saw the rise of popular preachers who argued that religious faith provided the solution to all manner of social and personal problems. Among Roman Catholics, the Archbishop Fulton J. Sheen of the Archdiocese of New York was a well-known figure as the longtime host of a radio show called The Catholic Hour, and, beginning in 1951, the impresario of an immensely popular weekly television program called Life is Worth Living.